feat(rule-tester): port checkDuplicateTestCases from ESLint

packages/rule-tester/package.json

@@ -51,6 +51,7 @@
  "@typescript-eslint/typescript-estree": "7.7.1",
  "@typescript-eslint/utils": "7.7.1",
  "ajv": "^6.12.6",
+ "json-stable-stringify-without-jsonify": "^1.0.1",
  "lodash.merge": "4.6.2",
  "semver": "^7.6.0"
  },
@@ -59,6 +60,7 @@
  "eslint": "^8.56.0"
  },
  "devDependencies": {
+ "@types/json-stable-stringify-without-jsonify": "^1.0.2",
  "@types/lodash.merge": "4.6.9",
  "@typescript-eslint/parser": "7.7.1",
  "chai": "^4.4.1",

packages/rule-tester/src/RuleTester.ts

@@ -20,6 +20,7 @@ import { Linter } from '@typescript-eslint/utils/ts-eslint';
 // we intentionally import from eslint here because we need to use the same class
 // that ESLint uses, not our custom override typed version
 import { SourceCode } from 'eslint';
+import stringify from 'json-stable-stringify-without-jsonify';
 import merge from 'lodash.merge';
 
 import { TestFramework } from './TestFramework';
@@ -40,6 +41,7 @@ import { getRuleOptionsSchema } from './utils/getRuleOptionsSchema';
 import { hasOwnProperty } from './utils/hasOwnProperty';
 import { interpolate } from './utils/interpolate';
 import { isReadonlyArray } from './utils/isReadonlyArray';
+import { isSerializable } from './utils/serialization';
 import * as SourceCodeFixer from './utils/SourceCodeFixer';
 import {
  emitLegacyRuleAPIWarning,
@@ -354,6 +356,9 @@ export class RuleTester extends TestFramework {
  );
  }
 
+ const seenValidTestCases = new Set<string>();
+ const seenInvalidTestCases = new Set<string>();
+
  if (typeof rule === 'function') {
  emitLegacyRuleAPIWarning(ruleName);
  }
@@ -403,7 +408,12 @@ export class RuleTester extends TestFramework {
  return valid.name;
  })();
  constructor[getTestMethod(valid)](sanitize(testName), () => {
- this.#testValidTemplate(ruleName, rule, valid);
+ this.#testValidTemplate(
+ ruleName,
+ rule,
+ valid,
+ seenValidTestCases,
+ );
  });
  });
  });
@@ -419,7 +429,12 @@ export class RuleTester extends TestFramework {
  return invalid.name;
  })();
  constructor[getTestMethod(invalid)](sanitize(name), () => {
- this.#testInvalidTemplate(ruleName, rule, invalid);
+ this.#testInvalidTemplate(
+ ruleName,
+ rule,
+ invalid,
+ seenInvalidTestCases,
+ );
  });
  });
  });
@@ -631,6 +646,7 @@ export class RuleTester extends TestFramework {
  ruleName: string,
  rule: RuleModule<MessageIds, Options>,
  itemIn: ValidTestCase<Options> | string,
+ seenValidTestCases: Set<string>,
  ): void {
  const item: ValidTestCase<Options> =
  typeof itemIn === 'object' ? itemIn : { code: itemIn };
@@ -646,6 +662,8 @@ export class RuleTester extends TestFramework {
  );
  }
 
+ checkDuplicateTestCase(item, seenValidTestCases);
+
  const result = this.runRuleForItem(ruleName, rule, item);
  const messages = result.messages;
 
@@ -673,6 +691,7 @@ export class RuleTester extends TestFramework {
  ruleName: string,
  rule: RuleModule<MessageIds, Options>,
  item: InvalidTestCase<MessageIds, Options>,
+ seenInvalidTestCases: Set<string>,
  ): void {
  assert.ok(
  typeof item.code === 'string',
@@ -693,6 +712,8 @@ export class RuleTester extends TestFramework {
  assert.fail('Invalid cases must have at least one error');
  }
 
+ checkDuplicateTestCase(item, seenInvalidTestCases);
+
  const ruleHasMetaMessages =
  hasOwnProperty(rule, 'meta') && hasOwnProperty(rule.meta, 'messages');
  const friendlyIDList = ruleHasMetaMessages
@@ -1030,6 +1051,30 @@ function assertASTDidntChange(beforeAST: unknown, afterAST: unknown): void {
  assert.deepStrictEqual(beforeAST, afterAST, 'Rule should not modify AST.');
 }
 
+/**
+ * Check if this test case is a duplicate of one we have seen before.
+ */
+function checkDuplicateTestCase(
+ item: unknown,
+ seenTestCases: Set<unknown>,
+): void {
+ if (!isSerializable(item)) {
+ /*
+ * If we can't serialize a test case (because it contains a function, RegExp, etc), skip the check.
+ * This might happen with properties like: options, plugins, settings, languageOptions.parser, languageOptions.parserOptions.
+ */
+ return;
+ }
+
+ const serializedTestCase = stringify(item);
+
+ assert(
+ !seenTestCases.has(serializedTestCase),
+ 'detected duplicate test case',
+ );
+ seenTestCases.add(serializedTestCase);
+}
+
 /**
  * Asserts that the message matches its expected value. If the expected
  * value is a regular expression, it is checked against the actual

packages/rule-tester/src/utils/serialization.ts

@@ -0,0 +1,42 @@
+/**
+ * Check if a value is a primitive or plain object created by the Object constructor.
+ */
+function isSerializablePrimitiveOrPlainObject(val: unknown): boolean {
+ return (
+ // eslint-disable-next-line eqeqeq
+ val === null ||
+ typeof val === 'string' ||
+ typeof val === 'boolean' ||
+ typeof val === 'number' ||
+ (typeof val === 'object' && val.constructor === Object) ||
+ Array.isArray(val)
+ );
+}
+
+/**
+ * Check if a value is serializable.
+ * Functions or objects like RegExp cannot be serialized by JSON.stringify().
+ * Inspired by: https://stackoverflow.com/questions/30579940/reliable-way-to-check-if-objects-is-serializable-in-javascript
+ */
+export function isSerializable(val: unknown): boolean {
+ if (!isSerializablePrimitiveOrPlainObject(val)) {
+ return false;
+ }
+ if (typeof val === 'object') {
+ const valAsObj = val as Record<string, unknown>;
+ for (const property in valAsObj) {
+ // TODO(#9028): use `Object.hasOwn` (used in eslint@9) once we upgrade to eslint@9
+ if (Object.prototype.hasOwnProperty.call(valAsObj, property)) {
+ if (!isSerializablePrimitiveOrPlainObject(valAsObj[property])) {
+ return false;
+ }
+ if (typeof valAsObj[property] === 'object') {
+ if (!isSerializable(valAsObj[property])) {
+ return false;
+ }
+ }
+ }
+ }
+ }
+ return true;
+}

yarn.lock

@@ -5197,6 +5197,13 @@ __metadata:
  languageName: node
  linkType: hard
 
+"@types/json-stable-stringify-without-jsonify@npm:^1.0.2":
+ version: 1.0.2
+ resolution: "@types/json-stable-stringify-without-jsonify@npm:1.0.2"
+ checksum: b8822ef38b1e845cca8151ef2baf5c99bc935364e94317b91eb1ffabb9280a0debd791b3b450f99e15bd121c0ecbecae926095b9f6b169e95a4659b4eb59f90f
+ languageName: node
+ linkType: hard
+
 "@types/json5@npm:^0.0.29":
  version: 0.0.29
  resolution: "@types/json5@npm:0.0.29"
@@ -5663,12 +5670,14 @@ __metadata:
  version: 0.0.0-use.local
  resolution: "@typescript-eslint/rule-tester@workspace:packages/rule-tester"
  dependencies:
+ "@types/json-stable-stringify-without-jsonify": ^1.0.2
  "@types/lodash.merge": 4.6.9
  "@typescript-eslint/parser": 7.7.1
  "@typescript-eslint/typescript-estree": 7.7.1
  "@typescript-eslint/utils": 7.7.1
  ajv: ^6.12.6
  chai: ^4.4.1
+ json-stable-stringify-without-jsonify: ^1.0.1
  lodash.merge: 4.6.2
  mocha: ^10.4.0
  semver: ^7.6.0